RFLP and cluster analysis of introgression of exotic germplasm into US maize inbreds

The use of exotic,germplasm in U.S. maize (Zea mays L.) breeding has a long history. There have been more failures to incorporate exotic germplasm int o maize than successes. Reasons for the lon rate Or success include: untest ed sources of exotic germplasm: low levels of agronomic fitness; a reduced effort compared to other maize breeding programs, and lack of information o n the most effective breeding methods to use when incorporating erotic germ plasm into adapted maize lines. Germplasm transfer fi om elite exotic inbre ds to U.S. inbreds has produced some positive results, but transfer likely could be enhanced greatly with the use of molecular markers. The first obje ctive of this study was to evaluate the agronomic performance of hybrids in volving maize lines developed from U.S. by Brazilian inbred crosses with on e or two backcrosses to the U.S. inbred parent. Evaluation over three years showed several hybrids involving US-Brazilian (USB) derived lines were sim ilar to check hybrids for grain yield and stalk lodging but slightly higher for harvest grain moisture. The second objective was use of Restriction Fr agment Length Polymorphism (RFLP) markers and cluster analysis to estimate and characterize the amount of Brazilian germplasm introgressed into the U. S. inbreds. Average percentages of RFLP variants from the Brazilian donor g ermplasm in USB backcross lines were generally similar to the theoretical e xpected values of the backcross method, but showed a considerable range of variation. The percentage of Brazilian RFLP fragments introgressed into 18 backcross-1 S-6 lines ranged fi om 1.7% to 42.1% and fur 16 backcross-2 SS lines ranged from 5% to 21.4%. The mean percentage of RFLP hybridization fr agments from each individual Brazilian germplasm source introgressed into t he different U.S. inbreds ranged fi om 7.5 to 22.4% with an overall mean of 12.9%. Cluster analysis of all lines produced II phenogram divided into ni ne groups corresponding to: the six U.S. inbreds and their derived USE back -cross lines: two groups of two Brazilian inbreds; and one Brazilian inbred . These results will serve as a basis for further efforts towards identific ation and use of molecular markers linked to desirable Brazilian alleles to facilitate their transfer into U.S. inbreds.